Histologic evaluation of tissue response to sintered lanthanum-containing hydroxyapatites subcutaneously implanted in rats.

Hydroxyapatite, lanthanum-containing hydroxyapatite, and lanthanum- and zirconium-containing hydroxyapatite discs were implanted subcutaneously in the backs of rats. The implanted discs and surrounding tissues were removed at 5 and 12 hours, and 1, 3, 7, 14, 30 and 60 days after implantation, and fixed in paraformaldehyde. Tissue samples were dehydrated and embedded in paraffin. Paraffin sections were cut and stained with hematoxylin and eosin, van Gieson's, and Masson's trichrome. The early tissue reaction was exudative due to fibrin deposition and infiltration by polymorphonuclear leukocytes and macrophages. The later reaction was characterized by the formation of fibrous tissue without inflammatory cell infiltration. The tissue reaction to all three types of material was identical by two months after implantation.